CavalliumDBEngine/src/main/java/it/cavallium/dbengine/database/collections/DatabaseSingleton.java

package it.cavallium.dbengine.database.collections;

import io.netty5.buffer.api.Buffer;
import io.netty5.buffer.api.Drop;
import io.netty5.buffer.api.Owned;
import io.netty5.buffer.api.Send;
import io.netty5.buffer.api.internal.ResourceSupport;
import it.cavallium.dbengine.client.BadBlock;
import it.cavallium.dbengine.client.CompositeSnapshot;
import it.cavallium.dbengine.database.Delta;
import it.cavallium.dbengine.database.LLRange;
import it.cavallium.dbengine.database.LLSingleton;
import it.cavallium.dbengine.database.LLSnapshot;
import it.cavallium.dbengine.database.LLUtils;
import it.cavallium.dbengine.database.UpdateReturnMode;
import it.cavallium.dbengine.database.serialization.SerializationException;
import it.cavallium.dbengine.database.serialization.SerializationFunction;
import it.cavallium.dbengine.database.serialization.Serializer;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.jetbrains.annotations.Nullable;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.publisher.SynchronousSink;

public class DatabaseSingleton<U> extends ResourceSupport<DatabaseStage<U>, DatabaseSingleton<U>> implements
		DatabaseStageEntry<U> {

	private static final Logger LOG = LogManager.getLogger(DatabaseSingleton.class);

	private static final Drop<DatabaseSingleton<?>> DROP = new Drop<>() {
		@Override
		public void drop(DatabaseSingleton<?> obj) {
			if (obj.onClose != null) {
				obj.onClose.run();
			}
		}

		@Override
		public Drop<DatabaseSingleton<?>> fork() {
			return this;
		}

		@Override
		public void attach(DatabaseSingleton<?> obj) {

		}
	};

	private final LLSingleton singleton;
	private final Serializer<U> serializer;

	private Runnable onClose;

	@SuppressWarnings({"unchecked", "rawtypes"})
	public DatabaseSingleton(LLSingleton singleton, Serializer<U> serializer,
			Runnable onClose) {
		super((Drop<DatabaseSingleton<U>>) (Drop) DROP);
		this.singleton = singleton;
		this.serializer = serializer;
		this.onClose = onClose;
	}

	private LLSnapshot resolveSnapshot(@Nullable CompositeSnapshot snapshot) {
		if (snapshot == null) {
			return null;
		} else {
			return snapshot.getSnapshot(singleton);
		}
	}

	private void deserializeValue(Buffer value, SynchronousSink<U> sink) {
		try {
			U deserializedValue;
			try (value) {
				deserializedValue = serializer.deserialize(value);
			}
			sink.next(deserializedValue);
		} catch (IndexOutOfBoundsException ex) {
			var exMessage = ex.getMessage();
			if (exMessage != null && exMessage.contains("read 0 to 0, write 0 to ")) {
				LOG.error("Unexpected zero-bytes value at "
						+ singleton.getDatabaseName() + ":" + singleton.getColumnName() + ":" + singleton.getName());
				sink.complete();
			} else {
				sink.error(ex);
			}
		} catch (SerializationException ex) {
			sink.error(ex);
		}
	}

	private Buffer serializeValue(U value) throws SerializationException {
		var valSizeHint = serializer.getSerializedSizeHint();
		if (valSizeHint == -1) valSizeHint = 128;
		var valBuf = singleton.getAllocator().allocate(valSizeHint);
		try {
			serializer.serialize(value, valBuf);
			return valBuf;
		} catch (Throwable ex) {
			valBuf.close();
			throw ex;
		}
	}

	@Override
	public Mono<U> get(@Nullable CompositeSnapshot snapshot, boolean existsAlmostCertainly) {
		return singleton.get(resolveSnapshot(snapshot))
				.handle(this::deserializeValue);
	}

	@Override
	public Mono<Void> set(U value) {
		return singleton.set(Mono.fromCallable(() -> serializeValue(value)));
	}

	@Override
	public Mono<U> setAndGetPrevious(U value) {
		return Flux
				.concat(singleton.get(null), singleton.set(Mono.fromCallable(() -> serializeValue(value))).then(Mono.empty()))
				.last()
				.handle(this::deserializeValue);
	}

	@Override
	public Mono<U> update(SerializationFunction<@Nullable U, @Nullable U> updater,
			UpdateReturnMode updateReturnMode) {
		return singleton
				.update((oldValueSer) -> {
					try (oldValueSer) {
						U result;
						if (oldValueSer == null) {
							result = updater.apply(null);
						} else {
							U deserializedValue = serializer.deserialize(oldValueSer);
							result = updater.apply(deserializedValue);
						}
						if (result == null) {
							return null;
						} else {
							return serializeValue(result);
						}
					}
				}, updateReturnMode)
				.handle(this::deserializeValue);
	}

	@Override
	public Mono<Delta<U>> updateAndGetDelta(SerializationFunction<@Nullable U, @Nullable U> updater) {
		return singleton
				.updateAndGetDelta((oldValueSer) -> {
					try (oldValueSer) {
						U result;
						if (oldValueSer == null) {
							result = updater.apply(null);
						} else {
							U deserializedValue = serializer.deserialize(oldValueSer);
							result = updater.apply(deserializedValue);
						}
						if (result == null) {
							return null;
						} else {
							return serializeValue(result);
						}
					}
				}).transform(mono -> LLUtils.mapLLDelta(mono, serializer::deserialize));
	}

	@Override
	public Mono<Void> clear() {
		return singleton.set(Mono.empty());
	}

	@Override
	public Mono<U> clearAndGetPrevious() {
		return Flux
				.concat(singleton.get(null), singleton.set(Mono.empty()).then(Mono.empty()))
				.last()
				.handle(this::deserializeValue);
	}

	@Override
	public Mono<Long> leavesCount(@Nullable CompositeSnapshot snapshot, boolean fast) {
		return singleton.get(null).map(unused -> 1L).defaultIfEmpty(0L);
	}

	@Override
	public Mono<Boolean> isEmpty(@Nullable CompositeSnapshot snapshot) {
		return singleton.get(null).map(t -> false).defaultIfEmpty(true);
	}

	@Override
	public Flux<BadBlock> badBlocks() {
		return Flux.empty();
	}

	@Override
	protected RuntimeException createResourceClosedException() {
		throw new IllegalStateException("Closed");
	}

	@Override
	protected Owned<DatabaseSingleton<U>> prepareSend() {
		var onClose = this.onClose;
		return drop -> {
			var instance = new DatabaseSingleton<>(singleton, serializer, onClose);
			drop.attach(instance);
			return instance;
		};
	}

	@Override
	protected void makeInaccessible() {
		this.onClose = null;
	}
}